We present two oscillator designs and a new amplification design which improves many characteristics of the dual-discharge tube tunable ArF excimer laser. We demonstrate bandwidths from (5–330 GHz) can be selected by appropriate choice of oscillator slit width and diffraction-grating dispersion. Amplification is achieved using three consecutive passes through the discharge tubes. This amplifier design decreases divergence (diffraction limit) and increases output energy (33%), locking efficiency (20%), range of tunability (40%), and spectral brightness (two orders-of-magnitude) when compared to the standard unstable-resonator amplifier.

A digital signal processing technique for interferometric peak localization in white light sensing systems is presented. The procedure is based on computational processing of the acquired interferometric signal using Fourier mathematical operations for fringe visibility improvement. Tests are made by computer simulations.

The phase plane method for deconvoluting fluorescence decay curves is generalized to the case of reference reconvolution. Particular cases of the reconvolution are considered: reconvolution via single exponential reference, analysis of two double exponential decays, and simultaneous analysis of parallel and perpendicular components of fluorescence with respect to each other. Results of simulation experiments, demonstrating possibilities of the proposed approach, are presented.

We investigate the uniformity of the plasma column produced on a multifin target which is designed for implementing a high gain recombination x-ray laser based on the controlled adiabatic expansion cooling scheme. It is shown that a plasma column, which is as uniform as that produced on a flat slab target, can be generated on a segmented target under an appropriate laser irradiation condition, and an enhancement of the on-axis emission of lasing lines is observed simultaneously, which can be attributed to an increase in laser gain. For the Li-like Al laser system, an increase of gain from 1.8 to 2.4 was evaluated by comparing the on-axis emission from the multifin target with that from the flat-slab target. However, a large nonuniformity is also observed when the laser condition is so changed that strong ion collisions between the neighboring plasmas appear. The extension of this target design to the shorter wavelength laser regime appears to be promising provided that both the target parameter and the driving laser condition are optimized.

The problem of controlling the temperature,pressure, and atmosphere around a solid sample for x-ray absorption spectroscopy, while accurately positioning it in the x-ray beam, has given rise to a wide range of designs. We describe here a new versatile design that provides excellent temperature control, and good hydrodynamics and corrosion resistance. Briefly, the cell comprises a stainless steel tube beam path, with a wafer sample positioned across the tube. Heat is supplied from an aluminum block that surrounds the tube. Gases for in situ sample treatment are flowed between fittings at the ends of the tube, and the dead volume is less than

A detection method for electron paramagnetic resonance spectroscopy is described that permits simultaneous acquisition of multiple in- and out-of-phase harmonics of the response to magnetic-field modulation for both dispersion and absorption: (i) conversion of the microwave carrier to an intermediate frequency (IF) carrier; (ii) subsampling of the IF carrier by an analog-to-digital converter four times in IF cycles where is an odd integer; (iii) dividing the digital words into two streams, odd indexes in one and even in the other, followed by sign inversion of every other word in each stream; and (iv) feeding the two streams to a computer for the digital equivalent of phase-sensitive detection (PSD). The system is broadbanded, in the frequency domain, with narrow banding for improved signal-to-noise ratio occurring only at the PSD step. All gains and phases are internally consistent. The method is demonstrated for a nitroxide spin label. A fundamental improvement is achieved by collecting more information than is possible using a single analog PSD.

A laser-driven particle accelerator, scaled to optical wavelengths, has a feature size many orders of magnitude smaller than a radio-frequency accelerator. However, similar to a radio-frequency accelerator, a laser-driven accelerator cell may have apertures to transmit electrons. We numerically calculate the acceleration field for a cylindrically focused, crossed-laser-beam linear accelerator with the presence of electron transit apertures. A 4-μm-width electron aperture decreases electron energy gain by 17%, and a 6-μm-width aperture decreases energy gain by 34% relative to a structure without apertures.

Recent instrumental improvements which successfully extend the time resolution of pulsed beamelectron diffraction to the picosecond regime are described. Based on modifications of an existing nanosecond apparatus, a new sample inlet system, electron pulse generation laser, and amplified detector have been incorporated into the design such that significant improvements in both the signal level and ultimate time resolution are achieved; an upper estimate of the electron pulse width is Enhancements are such that, for operation in the nanosecond time domain, an entire diffraction pattern over a useful range of scattering angles may be collected from a gas-phase sample in a single electron pulse.

An investigation to reduce the energy of the solid ion beam extracted from electron beam evaporation ion source for material modifications has been performed. The preliminary results have shown that the beam energy can be reduced to lower than 100 eV by a specially designed extraction system for carbon and nitrogen mixed ion beams. The beam current extracted is up to 30 mA for a small 20 mm extraction diameter ion source. It has been found that the extraction energy can be controlled by adjusting the bias voltage of the sample used for coating and the crucible potential. The extraction capability and the composition of the ion beam can also be controlled by changing the gas flow rate and the input power of the ion source. For carbon nitride films synthesized at low energy by this system, the results have shown to exhibit very high hardness values. The microhardness is over HK 6000 The principle of this ion source is described. The structure of the ion source, and the experimental results are also described in this article.

A calibration scheme based on ion-current measurement has been implemented for an electron-beam transition metaldepositionsource. Repeatable and practical means of positioning the source (tip), measuring the ion current, and determining the flux rate are given. Intrinsic variations in the structural parameters of the source and thermal effects which can modify the observed deposition rate were examined and compensated for. A stable regime where ion-beam current is directly proportional to the growth rate has been determined.

A novel charge exchangespectrometer using a dee-shaped region of parallel electric and magnetic fields was developed at the Princeton Plasma Physics Laboratory for neutral particle diagnostics on the TokamakFusion Test Reactor (TFTR). The spectrometer has an energy range of and provides mass-resolved energy spectra of and (or ) ion species simultaneously during a single discharge. The detector plane exhibits parallel rows of analyzed ions, each row containing the energy dispersed ions of a given mass-to-charge ratio. The detector consists of a large area microchannel plate (MCP) which is provided with three rectangular, semicontinuous active area strips, one coinciding with each of the mass rows for detection of and (or ) and each mass row has 75 energy channels. To suppress spurious signals attending operation of the plate in the magnetic fringe field of the spectrometer, the MCP was housed in a double-walled iron shield with a wire mesh ion entrance window. Using an accelerator neutron generator, the MCP neutron detection efficiency was measured to be and for 2.5 MeV-DD and 14 MeV-DT neutrons, respectively. The design and calibration of the spectrometer are described in detail, including the effect of MCP exposure to tritium, and results obtained during high performance D–D operation on TFTR are presented to illustrate the performance of the spectrometer. The spectrometers were not used during D–T plasma operation due to the cost of providing the required radiation shielding.

We describe a fast reciprocating probe drive, which has three main new features: (1) a detachable and modular probe head for easy maintenance, (2) a combination of high heat flux capability, high bandwidth, and low- materials construction, and (3) low weight, compact, inexpensive construction. The probe is mounted in a fast pneumatic drive in order to reach plasma regions of interest and remain inserted long enough to obtain good statistics while minimizing the heat flux to the tips and head. The drive is pneumatic and has been designed to be compact and reliable to comply with space and maintenance requirements of tokamaks. The probe described here has five tips which obtain a full spectrum of plasma parameters: electron temperature profile electron density profile floating potential profile poloidal electric field profile saturation current profile and their fluctuations up to 3 MHz. We describe the probe show radial profiles of various parameters. We compare the density and temperature data to that obtained with a helium beam. We also discuss the techniques to process the data optimally, particularly double probe data and profile fits.

A collector probe system at the TEXTOR-94 tokamak has been upgraded becoming a versatile tool in studies of erosion and deposition processes under plasma discharges. The reconstruction dealt with the distinct modification of the computer aided probe steering system and the collector probe head. The new operation system, based on a LabView environment, allows unlimited number of preprogrammed linear and angular probe movements and is applied for either integrated or time-resolved measurements of ion fluxes in the scrape-off plasma. Particular advantage is related to the possibility of such measurements during a selected part of a tokamak discharge, for instance the flat top, neutral beam injection phase, neon injection for plasma cooling, etc. The upgraded system and the results from some of the experiments, where the new possibilities have been beneficial, are presented in the article.

The Frascati Tokamak Upgrade (FTU) may require multiple high-speed pellet injection in order to achieve quasi-steady-state conditions. A research and development program was thus being pursued at ENEA Frascati, aimed at developing a multishot two-stage pellet injector (MPI), featuring eight “pipe gun” barrels and eight small two-stage pneumatic guns. According to FTU requirements, the final goal is to simultaneously produce up to eight pellets, and then deliver them during a plasma pulse (1 s) with any time schedule, at speeds in the 1–2.5 km/s range. A prototype was constructed and tested to demonstrate the feasibility of the concept, and optimize pellet formation and firing sequences. This laboratory facility was automatically operated by means of a programmable logic controller (PLC), and had a full eight-shot capability. However, it was equipped as a first approach with only four two-stage guns. In this article we will describe in detail the guidelines of the MPI prototype design, which were strongly influenced by some external constraints. We will also report on the results of the experimental campaign, during which the feasibility of such a two-stage MPI was demonstrated. Sequences of four intact pellets in the 1.2–1.6 mm size range, fired at time intervals of a few tens up to a few hundreds of ms, were routinely delivered in a laboratory experiment at injection speeds above 2.5 km/s, with good reproducibility and satisfactory aiming dispersion. Some preliminary effort to address the problem of propellant gas handling, based on an innovative approach, gave encouraging results, and work is in progress to carry out an experiment to definitely test the feasibility of this concept.

In an asymmetrical parallel plate reactor measurements of Ar radio-frequency (rf) plasmas are done with both single and triple probes. All measurements are carried out with the same probe construction and the probe systems are realized by changing probe circuit connections. Ar plasmas are generated with a frequency of 13.56 MHz at a pressure of 50 mTorr and a power of 20 W. In order to remove the alternative component the compensation circuits are connected to the probe system. It is found that there is a fairly good agreement between two probe characteristics obtained with the single and the triple probes. Influences of a time variation of the plasma potential on the results are reduced, but cannot be completely removed. The reason why the measurement results obtained with the single and the triple probes suffer from the same effect of the alternative component is explained using the equivalent circuits of the probe systems.

We present a transmission, fluorescence, and polarizationnear-field scanning optical microscope with shear-force feedback control that is small in size and simple to operate. This microscope features an ultrafine mechanical tip/sample approach with continuous manual submicron control over a range of several millimeters. The piezo-driven 12 μm scan range is complimented by a 4 mm coarse mechanical translation range in each direction. The construction materials used in the mechanical feedback loop have been carefully chosen for thermal compatibility in order to reduce differential expansion and contraction between the tip and sample. A unique pressure-fit sample mount allows for quick and reliable sample exchange. Shear-force feedback light is delivered to the scan head via an optical fiber so that a remote laser of any type may be used as a source. This dither light is collimated and refocused onto the tip, delivering a consistently small spot which is collected by a high numerical aperture objective. This new scan head incorporates an optical system which will permit the linearization of scan piezo response similar to a scheme used successfully with atomic force microscopy. This is designed to both overcome the piezo’s inherent hysteresis and to eliminate drift during long duration spatial scans or spectroscopic measurements at a single location. The scan head design offers added flexibility due to the use of optical fibers to deliver the dither and scan linearization light, and functions in any orientation for use in conjunction with upright or inverted optical microscopes.

We have designed and constructed a low temperature, ultrahigh vacuum scanning tunneling microscope(STM), taking extreme measures to isolate the microscope from acoustic, vibrational, and electronic noise. We combined a 4 K STM with line-of-sight dosing to enable one to position the crystal surface in front of an impinging molecular beam as in scattering experiments. Due to the mechanical stability of the instrument and the minimal thermal drift associated with working at 4 K we are able to locate and to image repeatedly isolated adsorbates and atomic-scale structures, such as step edges, for extended periods days. The instrument has been designed for the topographic and spectroscopic characterization of atoms and molecules on metal and semiconductor surfaces, for the investigation of the mechanism by which the STM images adsorbates on surfaces, and for inelastic electron tunneling spectroscopy of single molecules.

With the increasing popularity of the scanning tunneling microscope(STM) in surface science, many ideas for additional and new technical features have been proposed. The work herein contributes to this evolution with a special STM design. The STM described is part of an experimental apparatus for thin film growth investigations in ultrahigh vacuum. Besides the STM, the apparatus includes facilities for thermal desorptionspectroscopy and Auger electron spectroscopy and a Kelvin probe for measuring dynamic work function changes. The Kelvin probe is optimized for gas adsorption experiments as well as for in situfilm growth investigations during metal deposition. These added features combined with the STM and easy sample transfer yield a new powerful tool for in situ controlled preparation and extensive characterization of thin films. In the present work we describe the novel features of this STM and we demonstrate the efficiency of the whole system by giving a few representative results.

X-ray diffraction on surface acoustic waves with tunable wavelength provides a way to perform beam scannings. 1D and 2D space scannings of x-ray beams by this method are presented. The feasibility of a purely optical method to perform scanning x-ray imaging without any mechanical movement is discussed.

A practical cryogenic probehead for NMR microscopy is described. The superconducting coil is composed of a layer on a substrate. The probehead consists of a continuous flow cryostate with a room temperature bore for the sample. For better performance the sample can be positioned in the center of the coil. To evaluate the gain in sensitivity, spin-echoimages are presented which compare the (YBCO) resonator to a room temperature and a cryogenicCu resonator. These results are corroborated through theoretical calculations. To estimate the potential of superconducting coils for NMR microscopy we have made a theoretical comparison of an YBCO resonator with a microscopic solenoid with three winding.